Fuel cells are electrochemical devices which convert the chemical energy of a chemical reaction directly into electrical energy. A typical fuel cell consists of an electrolyte membrane and anode and cathode compartments sandwiching the electrolyte membrane therebetween, in which fuel gas is fed continuously to the anode compartment, air is fed continuously to the cathode compartment, and oxygen from air and hydrogen contained in the fuel gas electrochemically reacts to generate electric power. If gas shortage occurs in a local region in the compartment, power output of the fuel cell drops, which may result in overcurrent causing cells to be damaged. It is required in control of a fuel cell to have a function to detect the presence of such deteriorated operating condition and recover the deteriorated operating condition, so as to preclude the cells from being damaged.
Japanese Patent Application Laid-Open Publication No. 6-243882 discloses a control method for a fuel cell stack compartmentalized into a plurality of cell sections, in which output voltages of the cell sections are monitored and when the lowest voltage in the detected drops below a predetermined value, the operation of the fuel cell stack is stopped for protecting the system regardless of the magnitude of load on the fuel cell.